Transmission system



Dec.. 19, 1922. 1,438,938. J. F.l BALDWIN, 1... H TRANSMISSION SYSTEM.

FILED MAR. 29, 1920.

.x fra/3M @6l/mm an Patented Dec. 19, 1922.

ITED I S'lii'l'liisi PATE `l` JOHN FRANK BALDWIN, JR., OF EAST ORANGE,'NEW JERSEY, ASSIG-NOR T0 WESTERN ELECTRIC COMEANY, INCORPORATED, OF NEW YOIIRJK,V N. Y., A CORPORATION OF NEW YORK. TRANSMISSION SYSTEM.

Application led March 29, 1920. Serial No. 369,653.

To all whom t may concern.' duced to a negligible amount by inserting Be it known that I, JoiiN FRANK BALD- washers of magnetic material'between adwiN, Jr., a citizen ot the United States, jacent coils. 4 residing at East Orange, in the county ot' It has been found, however, that the in- Essex, State of New Jersey, have invented sertionof a washer between the two groups 60 certain new and useful Improvements iii ot coils repeating in opposite directions is Transmission Systems, ot which the follownot sufficient to reduce the cross-talk thereing is a full, clear, concise, and exact de- Abetween toa negligible amount, owing to scription. the fact that the cross-talk between coils This invention relates to transmission sys transmitting in opposite directions is con- 65 tems, and more particularly to transmission siderably greater than .that occurring be- Systems of the type knownvas four-wire retween coils transmitting in the saine direcpeater systems. tion. ln accordance with this invention it `Where a vnumber of four-'wire transmisis proposed to substantially eliminate the: 1'5 sion systems parallel each other, serious cross-talk occurring between the two groups 70 cross-talk diiiculties are encountered owingV transmitting in opposite directions by to the high degree of amplification that it grounding a shield or washer located beis desirable to employ in these circuits, and tween the two groups. it is one of the objects of this invention This invention will be better understood to reduce this cross-talk to a minimum. by reference to the following detailed de- 75 Other further objects will be clear from the sci'iptiontaken in connection with the acdetailed description to be given later. companying drawings vin which Fig. 1, Arepln four-wire transmission systems as is reseiits a plurality of four-wire transmiswell known, two separate transmission lines sion circuits; Fig. 2, represents a type of are employed, one for transmitting in each loading coil assembly which may be em- 80 direction, each line including one or more ployed in loading the side'circuits of Fig. one-way repeaters for amplifying the trans- 1, and Fig. 3, represents a type of loading mitted current. When a number of circuits coil assembly which may be employed in of this character closely parallel each other. loading the phantom circuits of the fourthe current transmitted in a line employed wire -transmission lines shown in F1g.1. f 85 for transmission in one direction induces l Fig. 1, illustrates a plurality of fourcross-talk in all of the transmission lines wire transmission lines, 5, 6, 7 and 8. Loadassociated therewith'. It has been found, ing coils 9, 10, 11, 12,- 13, 14, 15 and 1? may however, that the cross-talk currents inbc employed 'for loading the side circuits 17,

duced in linestransmitting in the opposite 18, 19, 20, 21, 22, 23 and 24 respectively'of 90 direction are generally much more serious the four-wire transmission' circuits. Side .than those induced in lines transmitting in circuits 17 to 20 inclusive may be employed the same direction. This invention is confor transmitting currents in one direction, cerned chiefly with. the reduction of crosswhile side circuits 21 to 24 inclusive may 40 talk induced between lines transmitting in be employed for transmitting signaling cur- 95 opposite directions, rents in the oppositedirection.

lnv loading four-wire transmission lines, Fig. 2, illustrates a loading coil assembly it has been a common expedient to inclose which may be employed for housing .the in a common pot or" casing, loading coils various side circuit loading 'coils required for a .plurality of lines. It has been hitherfor the four-wire transmission lines 5`, 6, 100

.to proposed to reduce the cross-talk between 7 and 8. 'The casing 30 contains a spinadjacent coils in a common casing by so dle 31 on which is mounted loading coils grouping the coils in the casing that the 9 to 16 inclusive. Loading coils 9, to 12 coils of the lines transmitting 'in one diinclusive which transmit in the same direcrection will be in one group and the coils. tion have been placed in one group, and 105 fory lines transmitting in the opposite di- 'loading coils 13 to 16 inclusive have been -rection will'be'in a second group, the two placed in aA second group. The connecting groups being carried bythe same spindle. Wires for the various loading coils contained The cross-talkbetween adjacent coils transin the casing 30 may be led'out through a mitting in the same direction may be recommon cable 32. 11o

transmitting in the opposite direction for al similar purpose. l

It has been found, however, that the inser- .tion of a magnetic washer between the group of coils 9 to 12 inclusive and the group of coils 13 to 16 inclusive, while substantially eliminating any stray magnetic field between the two groups is not sufficient to reduce to a negligible amount the cross-4 talk occurring between the groups due to the capacity effect existing therebetween which tends to set up leakage currents. It is truey that it would bel possible to reduce this capacity effect to a negligible amount by greatly increasing the distance between the -two groups, but such a wide spacing would not be possible when' it is necessary to make the assembly of the loadlng coils as compact as possible. In accordance with this invention this undesired electrostatic field between the two groups may be substantially eliminated by grounding the magnetic washer 36 located therebetween. This grounding may be accomplished by connecting the magnetic washer tothe external casing or housing 3U. The thickness of the washer 36 need not be more than a small fraction of the width of one of the loading coils in order to give satisfactory results.

Fig. 3, illustrates the housing for a phantom loading coilassembly which may be employed in the'circuits of Fig. 1, in case it is desired to phantom the four-wire circuits.V As is well known it is possible to -transmit in one direction employing the four wires of system 5 in parallel and to trans- `mit in the opposite direction employing for example the four wires of system 7 in par# allel. The four wires of system 6 may also be employed in parallel for transmitting in one direction, Awhile the four wires of system 8, may be emploayed in parallel for transmitting in the opposite direction. The casing or housing 40 shows the phantom loading coils 41, 42, 43 and 44 for the four wire systems 5, 6, 7 and 8 mounted on a common spindle in a manner similar to the arrangement for the side circuit coils. Adjacent coils in the casing 40 are shielded from each other by means of magnetic washers 47, 48

and 49. In this case, it has been found necessary to ground each of the washers 47, 48 and 49, in order to eliminate the capacity effects between neighboring coils so as to avoid cross-talk.. l

It is `obvious thatthis invention may be applied to types of transmission systems other than the type described above without departing in anywise fromthe spirit of thisl inventionl defined in the appended claims.

lVhat is claimed is:

1. A transmission system comprising :1 plurality of conductors, a pluralityl of loading coils in said conductors, afcommon housing for said loading coils, two

of said loading coils being separated` from each other a distance less than thel width of one of said loading coils, and means between said two loading coils for substantially eliminating the electrostatic field therebetween. l

2'. A transmission system including a plurality of conductors, certain of which are used for transmission in onedirection and others of which are used'for -transmission inthe opposite direction, loading coils in said conductors, said loading coils being arranged in groups so that loading coils con-- ductors used for ltransmission in opposite directions will be 1n separate groups, and a grounded metallic shield between said groups. i

3. A rality of conductors certain of which are used for transmission in one direction and, others of which are used for transmission inthe opposite direction, loading coils .in said conductors,said loading coilsbeing arranged in groups so that loading' coils in conductors used for transmission in opposite directions will be in Wseparate groups, said two groups'being separated from each other a distance less than the width of one of said loading coils, and means between said groups for substantially eliminating the electrostatic eld therebetween.

4. In combination, a plurality of` loading coils concentrically arranged, a common housing for said coils, two of said coils being separated from each other a distance less than the width of one of saidcoils, and a grounded metallic shield between said twolast-mentioned coils.

In witness whereof, I hereunto subscribe my name this 25th day of March, A. D. 1920.

J. FRANK BALDWIN, JR.

transmission system including a plu- 

